In general, a paper machine includes a forming section where a thin slurry of e.g. water and fiber are expressed onto a relatively permeable closed loop forming fabric, also known as a fourdrinier fabric. Free water drains through the forming fabric, leaving a more or less consolidated matt of the fibers on the forming fabric.
From the forming fabric, the consolidated, but still quite wet, matt of fibers is transferred to a papermaking felt. Like the forming fabric, the felt is configured as a closed loop. Typically, the felt carries the consolidated matt of fibers of the web being formed through a press section, where additional water is removed from the matt by mechanically squeezing.
A typical felt comprises a substrate having opposing major surfaces, and one or more batts of fibrous material needled into, or otherwise assembled to, the opposing major surfaces of the substrate. In making the felt, typically the substrate is first woven in a closed loop configuration. More than one substrate web can be used to form the internal structure of the substrate, after which the batts of fibrous material are needled into the substrate from the opposing major surfaces of the substrate.
Depending on the configuration, the composition, and the spacing of the batt fibers, the fibers perform a variety of functions, including influencing the rate of removal of water from the web of paper being formed, and at least influencing the final surface texture of the paper web being formed.
From the felt, the web of paper being formed typically passes into the dryer section of the paper machine, and thence to the winder where the formed and dried web of paper is wound onto a roll.
In any web of paper being formed, the texture and other surface properties, are influenced by texture and other surface properties of the felt. Such surface properties, as well as the interior characteristics such as the overall density and water drainage properties should be uniform. Variations in either the substrate web or the fibers needled into the substrate web are typically reflected in the paper web made with the felt.
Substantial efficiencies are realized as processing speeds are increased in paper making, and in paper converting, processes. In such processes, it is critical that the paper user, or paper converter, be able to rely on uniformity, both along the length and along the width, of the paper web produced at the paper machine.
Accordingly, in making the closed loop felt, the felt should present, to the web being formed into a web of paper, physical properties that are functionally uniform about the entire area of the surface of the felt which contacts the web.
Various methods are known for fabricating the felt as an endless loop. For example, U.S. Pat. No. 4,737,241 Gulya teaches a method using a pin joint to close the loop, across the width of the web, in a previously-formed substrate web having opposing first and second ends. The areas at and immediately adjacent to the pin joint, by their very nature, have structural and thus physical properties that differ somewhat from the properties associated with the remainder of the felt. In all cases, such pin joint felts carry at least the potential that the different properties at the pin joint might be transferred to the paper web manufactured with such felts.
It is known to weave the substrate web for the felt as a closed loop on a shuttle loom appropriately designed for such closed loop weaving. In conventional felts, the closed loop weaving process is often preferred because the felt is fabricated as a closed loop having no ends Such a felt has no joint across its width, and correspondingly no potential for variation of the properties in the felt at the joint.
While a felt fabricated as a closed loop is superior to pin joint felts in that there is no cross-directional joint, weaving a felt substrate web in a closed loop configuration entails significant set-up cost which may be attenuated by weaving a substrate web precursor as a flat fabric, and subsequently forming the flat-woven fabric into an endless loop in a fuse bonding process.
In general, weaving includes a first step of threading an array of warp threads into the weaving machine, followed by the actual thread-by-thread interdigitation of the weft threads into the array of warp threads as the warp threads are advanced past the shuttle or other carrier of weft thread. Compared to flat-woven fabrics, the process of incorporating threads into a fabric being woven in a closed loop configuration is in general slower than flat weaving the same fabric.
Overlooking for the moment the issue of fabricating the substrate web into a closed loop, it is entirely possible for a felt manufacturer to predict with reasonable accuracy the weave patterns and materials of substrate webs which will be needed for manufacturing purposes in the near term future e.g. six months or less. It is much more difficult to predict the length and width requirements of the specific felts which will need to be manufactured in the near term future. Until the length and width requirements of a particular felt are known, it is generally not feasible to begin set-up or weaving of a closed loop substrate web.
Accordingly, the entire process of assembling a felt, including weaving of the substrate web is typically delayed until the manufacturer receives the length and width specifications for the finished felt. As a result, where a pin-joint felt is not acceptable, felt manufacturers are effectively precluded from stockpiling standard woven substrate web materials. They must wait for the customer's specifications and order.
While the felt needed for any given paper machine is typically unique to that machine, most felt substrates incorporate one or more of a relatively small number of weave patterns, using threads according to one or more of a relatively small number of types of materials and/or threads. Thus, in principle, if it were feasible to form the flat-woven substrate web precursor material into a closed loop configuration after manufacture of the substrate web precursor material, the felt manufacturer could reasonably flat weave, and stockpile in e.g. roll form, a variety of the more common substrate web precursor materials in e.g. a relatively small number of weave patterns and materials, against anticipated but not yet received orders.
Such pre-manufacture of the substrate web material would carry attendant cost advantages associated with longer weaving runs without intervening set-up costs, and shorter lead times between receipt of the order and shipment of the finished felt. The felt manufacturer could stockpile a supply of standard substrate webs, and draw appropriate substrate web precursor material from the stockpiled rolls when an order is received.
It is an object of the invention to provide a novel woven felt substrate web, and a felt made therewith, the substrate web having a fuse bonded joint extending across the width of the substrate web, the joint having an outer surface, and texture in the surface, along the width of the web, corresponding with the pattern of the weave.
It is another object of the invention to provide a novel woven felt substrate web, and a felt made therewith, the substrate web having a fuse bonded joint extending across the width of the substrate web, the joint having minimal, if any, residual elements of a crown on one surface of the substrate web, and minimal, if any, residual elements of a valley on the opposing surface.
It is yet another object to provide a novel papermaking felt having a substrate web, and a joint in the substrate web, the machine direction tensile strength generally along the length of the substrate web being relatively greater than the machine direction tensile strength at the joint.
It is still another object to provide a novel papermaking felt, including first and second substrate web elements in face-to-face relation with each other, each having a transverse joint, with the joints spaced from each other.
A further object is to provide a novel method of making a papermaking felt from a flat-woven precursor web, including severing a web element, and forming the web into a closed loop with a fuse bonded joint.
Yet another object is to provide a novel method of making a papermaking felt from a flat-woven precursor web, including severing a web element, superposing end portions of the web element on each other, severing the ends, fuse-bonding the ends to each other, rotating the edge portions about the fuse-bonded ends, and assembling batts of fibrous material to opposing surfaces of the substrate web so formed.
Still another object is to provide a novel method of making a papermaking felt from a flat-woven precursor web, including severing a web element, superposing end portions of the web element on each other, and fuse bonding the ends of the web element to each other.
An additional object is to provide a novel method of making a papermaking felt including fabricating at least first and second substrate web precursors, subsequently specifying the properties of the felt and selecting one of the substrate web precursors, severing a substrate web element from the selected precursor, and forming a fuse-bonded joint in the web precursor to make the closed loop substrate web.
A still additional object is to provide a novel method of making paper, using a felt with a crown, wherein the crown is displaced from the surface which receives the paper web being formed.
Yet a further object is to provide a method of making a papermaking felt including weaving a substrate web precursor on a shuttle-less loom, severing a web element from the precursor, fuse bonding ends of the web element to each other to make the web element into a closed loop configuration comprising the substrate web, and then assembling batts of fibrous material to opposing surfaces of the substrate web.